1. Field of the Invention
This invention relates generally to telefacsimile machines and coding methods. More particularly, the invention relates to a telefacsimile machine having the ability to distinguish recognizable characters from unknown graphics, and to transmit codes for the recognizable characters with less data than that required by bit maps employed in known devices.
2. Related Art
Known telefacsimile or fax machines scan a document to produce pixel data. This pixel data is then compressed and sent over communications media such as telephone lines to a receiving fax machine. A problem with such telefacsimile machines is the lack of data compression for characters and the lack of efficient coding for character data.
U.S. Pat. No. 4,410,916 issued to Pratt discloses a dual mode telefacsimile compression technique, wherein spatially isolated black and white pixel patterns expected to recur in a document are extracted and coded by a matching process. A trial block area around a block pixel is examined to isolate symbols. Isolated symbols are labeled and a set of measured features is used to build a library. Each symbol subsequently found in trial blocks of the scan is compared to the features of the blocks to eliminate unworthy symbols from a template matching process If the matching error falls below a threshold, the identification of the matching library number is stored for later coding. If no symbol is found within a trial block, the block is encoded as residue using a modified relative address code and processed separately. The symbols' library identification codes and residue codes and the codes of unsuccessfully compared symbols are transmitted to receivers. The specialized coding in Pratt is quite slow due to the need to perform extensive template matching for each character. Pratt does not distinguish text from graphics, and fails to provide flexible operation in other modes, such as transmission of bit maps, so that communication is only possible among similarly equipped units.
U.S. Pat. No. 4,566,127 to Sekiya discloses a telefacsimile having an optical character reader and a central processing unit which provide coding character information and a telefacsimile mode. However, Sekiya is limited to operation with documents of a predetermined format in which character groups having predetermined attributes are disposed in a first location of the document and images having predetermined attributes are disposed in a predetermined second location
U.S. Pat. No. 4,922,545 to Endo discloses a telefacsimile image coding method in which an input image pattern which occurs once is sequentially scanned and conventionally encoded. Patterns appearing twice or more, according to a matching pattern, are encoded by position coordinates and a library identification code is added at the time the pattern is registered in a library. This system is primarily a handwriting recognition system, and there is no provision for flexible operation with units not similarly equipped.